A number of references describe the effects of electric current upon planktonic microorganisms (Nature, Sale, Hamilton, Pareilleux, Rowley (1972), Shimada (1982), Shimada (1985), Ebert). Various causes for the lethal effects of electric current are proposed. Rowley (1974) describes the effects of direct current in reducing the viability of infecting microorganisms using a rabbit model. The application of direct current to a surface wound was shown to enhance antibiotic activity.
Iontophoretic devices are also well known (U.S. Pat. No. 4,411,648, Davis (1982), Rootman, Hobden, Davis (1989)). Iontophoresis is a process whereby an agent can be driven into surrounding tissue or a fluid path by application of an electric current.
None of the previously described references describe methods or devices which utilize electric current to kill or reduce biofilms. A biofilm is a conglomerate of microbial organisms embedded in a highly hydrated matrix of exopolymers, typically polysaccharides, and other macromolecules (Costerton 1981). Biofilms may contain either single or multiple microbial species and readily adhere to such diverse surfaces as river rocks, soil, pipelines, teeth, mucous membranes, and medical implants (Costerton, 1987). By some estimates biofilm-associated cells outnumber planktonic cells of the same species by a ratio of 1000-10,000:1 in some environments.
Prevention of colonization by and eradication of biofilm-associated microorganisms is an important, and often difficult to solve, problem in medicine. Unlike planktonic organisms, which are relatively susceptible to biocides, e.g., antibiotics, the structural matrix established during biofilm formation can make the colonizing cells able to withstand normal treatment doses of a biocide. It is known that when organisms are isolated from biofilms and then grown in planktonic culture, they lose many of the characteristics associated with the progenitor cells, in particular, the ability to produce a glycocalyx (Costerton, 1987). In the biofilm, the glycocalyx matrix appears to serve as a barrier which protects and isolates the microorganisms from host defense mechanisms, such as antibodies and phagocytes, as well as from antimicrobial agents including surfactants, biocides and antibiotics (Costerton, 1981). In one study, biofilm-associated bacteria were able to survive a concentration of antibiotic 20 times the concentration effective to eliminate the same species of bacteria grown in planktonic culture (Nickel, 1985).
Biofilm infections can occur in a variety of disease conditions. In some tissue infections, such as prostatitis, the infective bacterium is capable of growing in the infected tissue in both biofilm (sessile) and circulating (planktonic) form (Costerton, 1987). Although growth of the planktonic cells can be controlled by antibiotic treatment, the biofilm itself may be refractory to treatment, providing, in effect, a reservoir of infection which can lead to recurrence of the infection after antibiotic treatment.
Biofilm formation can also be a serious complication in bioimplants, such as bone prosthesis, heart valves, pacemakers and the like. Biofilm formation on exposed surfaces of a bioimplant can degrade the function of the implant (Passerini), as in the case of implanted valves, lead to serious joint or bone infections, as in the case of a bone prosthesis (Gristina), and in all cases, provide a source of difficult-to-treat septic infection (Jacques).